Process for the manufacture of an electrical contact point

ABSTRACT

IMPROVED PROCESS OF PRODUCING CONTACTS HAVING A BASE SUPPORT OR SUBSTRATE COATED ON AT LEAST PART OF AT LEAST ONE SURFACE WITH A HARD TO FORM METAL SUCH AS TUNGSTEN, RHENIUM, MOLYBDENUM, RUTHENIUM, IRIDIUM OR AN ALLOY THEREOF WHEREIN THE METAL COATING MATERIAL IS PROVIDED AS AT LEAST THE INSIDE SURFACE OF A CYLINDER AND POSSIBLY ALSO AS AN AXIAL ROD INTHE CYLINDER, ATTACHED TO A HIGH FREQUENCY GENERATOR WHICH CYLINDER HAS A LONGITUNDINAL SLIT THEREIN, A PLASMA IS GENERATED BY THE HIGH FREQUENCY GENERATOR WHICH ATOMIZES THE METAL AND DISCHARGES SUCH THROUGH THE SLIT ONTO A SUITABLE SUBSTRATE WHICH MAY BE MADKED, IF DESIRED. THE PROCESS IS SUITABLY CARRIED OUT IN A HERMETICALLY SEALED CHAMBER HAVING VACUUM PUMPING MEANS ATTCHED THERETO AND GAS ADMITTANCE MEANS ATTACHED THERETO WHEREBY THE PRESSURE CAN BE REGULATED TO 10-2 TO 1MM. HG A AND THE ATMOSPHERE CAN BE REGULATED AS DESIRED.

Dec. 28, 1971 w. REICHELT 3,630,872

PROCESS FOR THE MANUFACTURE OF AN ELECTRICAL CONTACT POINT Filed Sept. 9, 1969 'IIIIIIIIIIIIIIIJ INVENTOR WALTER REICHELT BURGESS. DINKLAGE & SPRUNG ATTORNEYS.

United States Patent 3,630,872 PROCESS FOR THE MANUFACTURE OF AN ELECTRICAL CONTACT POINT Walter Reichelt, Hanan am Main, Germany, assignor to W. C. Heraeus G.m.b.H. Patentabteilung, Hanan, German Filed Sept. 9, 1969, Ser. No. 856,932 Claims priority, application Germany, Oct. 14, 1968, P 18 02 932.8 Int. Cl. C23c 15/00 US. Cl. 204-192 9 Claims ABSTRACT OF THE DISCLOSURE Improved process of producing contacts having a base support or substrate coated on at least part of at least one surface with a hard to form metal such as tungsten, rhenium, molybdenum, ruthenium, iridium or an alloy thereof wherein the metal coating material is provided as at least the inside surface of a cylinder and possibly also as an axial rod in the cylinder, attached to a high frequency generator which cylinder has a longitudinal slit therein, a plasma is generated by the high frequency generator which atomizes the metal and discharges such through the slit onto a suitable substrate which may be masked, if desired. The process is suitably carried out in a hermetically sealed chamber having vacuum pumping means attached thereto and gas admittance means attached thereto whereby the pressure can be regulated to 10- to 1 mm. Hg A and the atmosphere can be regulated as desired.

This invention relates to a process for manufacturing an electric switch contact point or a switch contact tongue or spring for the low-current-low-voltage art.

The relays of the electrical low-current-voltage art, particularly those of the communications art, are increasingly being constructed as magnetically operated inert-gas relays. The contact materials must satisfy very exacting requirements if the long life expectancy, on the order of 10'' to 10 switching cycles which is demanded of the relays is to be achieved. The contact point materials used are, for example, hard-to-form metals such as tungsten, molybdenum, rhenium, ruthenium or an alloy of these metals. Use is made particularl of switch contact points or switch contact tongues or springs which consist of a metal support coated in part with the contact material, at least on one face. Suitable materials for the support are ferromagnetic materials, such as iron-nickel alloys, for example, but others are German silver, brass, bronze or pure metals such as copper, silver or nickel. Good results as regards contact resistance and life expectancy are achieved when the support is coated with a hard-to-form metal or an alloy of such a metal (that is, an alloy whose principal component is the hard-to-form metal), and then this contact material coating is additionally coated with a layer of a noble metal such as gold, silver, platinum, or a noble-metal based alloy (that is, an alloy whose main component is a noble metal of this group), which will not stick or weld in making the contact, for the purpose of reducing friction and the erosion associated therewith. While this layer of noble metal or noble metal alloy can be relatively thin, e.g., 1 or a few microns thick, the contact layer of hard-to-form metal applied to the support should often have about ten times that thickness, i.e., it should have a thickness on the order of about 10 microns, for example.

The manufacture of these switch contacts which are needed in extremely large quantities, especially in the case of those to be used in the communications art, presents an especially diflicult problem.

The contact materials named above, those of the group tungsten, molybdenum, rhenium and ruthenium, including alloys based on metal of this group, are difficult to form, so that the manufacture of such contacts by punching or stamping them from sheets or strips of the support material plated with the contact material by a roll laminating method entails many problems, such as variations in thickness and roll textures. Furthermore, the contact surface, which must be very precise in the case of relays used in the communications art, often does not satisfy the high quality requirements of this art. Inasmuch as galvanic plating processes have not been successful, attempts have also been made to produce the contact coating on the metal support by condensation from the gaseous phase, that is, metal vapor deposition.

It has, therefore, previously been proposed that the contact coating be produced on the support by using electron beams to evaporate the contact material in a hermetically sealed envelope in which a high vacuum is maintained, and then condensing the evaporated contact material on the support. It has been found, however, that control of the temperature of the condensation surface represents a problem that is extremely hard to solve. If relatively thick coatings, amounting for example, to 10 microns and more, are to be produced on the support from materials that are difficult to evaporate, such as tungsten, molybdenum or rhenium this problem becomes increasingly diiiicult. In order to be able to efiiciently utilize the vapor produced by the electron beam bombardment, the distance between the vapor source and the support must be as small as possible. In that case, however, the effect produced on the support by the thermal radiation emitted by the molten metal at a temperature of at least 3600 C. is exceedingly great, so that special measures must be taken to remove the radiated heat. Furthermore, the strong thermal radiation exercises a gas desorbing action in all areas of the inside of the envelope which are struck by the radiation, so that very large vacuum pump sets are needed to maintain the high vacuum. Too high a pressure results in defective, brittle coatings, especially in the case of tungsten or molybdenum. Also, strong annoying currents of stray electrons become apparent. Furthermore, the rate of evaporation of these metals is very low, even in the case of high electron beam power, because the heat losses, due on the one hand to the water-cooled evaporation crucible and on the other hand to thermal radiation from the surface of the molten metal, are extremely great. Also, the production of contact coatings from alloys by means of the electron beam evaporation process presents considerable difficulties as regards maintaining a uniform allo composition within the entire contact layer.

The evaporation of platinum, palladium, rhodium or an alloy based on a metal of this group at reduced pressure for the purpose of making contact coatings entails great difiiculty because in the molten, superheated state, such as that involved in the evaporation process, these metals react with ordinary crucible materials.

Attempts to produce contact coatings by using methods employed in the prior art for other purposes and referred to as cathodic sputtering have shown that, whether it be a diode, triode or tetrode process, so long a time is needed to produce a sufficiently thick coating on the support that the process must 'be considered impractical for the manufacture of switch contacts in the large quantities needed, because it is uneconomical, if for no other reason.

The invention is directed to the problem of finding a process which can be performed without great technical expense and which will make it possible to produce a relatively thick coating of suitable contact metal on a metal support in an economically reasonable manner. Such contacts are needed in extremely large quantities, so that manufacture thereof at low cost has been a real problem for a long time.

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These problems are solved by a process for the manufacture of an electrical switching contact point or a switching contact tongue or spring for the low-current-low-voltage art, consisting of a metal support which is partially coated on at least one face with a contact material under reduced pressure in a hermetically sealed vessel, which process comprises atomizing a metallic material by means of a high-frequency plasma discharge in the hermetically sealed vessel, in which a pure noble-gas atmosphere or a noble gas-hydrogen atmosphere containing about 20 vol. percent hydrogen, or a noble-gas. atmosphere with a gaseous additive which reacts with the atomized metallic material to form a compound such as a carbide, boride or nitride, is maintained at a pressure ranging from 10- mm. Hg to 1 mm. Hg, and depositing a contact layer composed of the atomized metallic material or of a reaction product of this material with the gaseous additive on the support in a thickness of about 1 to 100 microns, preferably about 5 to 30 microns. The process of the invention has proven particularly desirable for high-melting, hard-to-form metals of the group molybdenum, tungsten, rhenium, ruthenium, or iridium, or alloys containing as principal component a metal of this group, or alloys of at least two metals of this group. The process of the invention can also be used advantageously for metals of the group platmum, palladium or rhodium, or for alloys containing as principal component a metal of this group, because in this process no crucible is needed to contain the metal and so undesirable reactions of the aforesaid metals with the crucible material, such as have been observed in the evaporation of these metals under reduced pressure, are avoided. The process of the invention has also produced very good results in the manufacture of contact coatings from an alloy of gold or silver.

According to another feature essential to the invention, the high-frequency plasma discharge is produced in a slitted hollow cylinder disposed in the vessel, the inner peripheral surface of said cylinder consisting at least of the metallic material that is to be atomized, and it has proved desirable to dispose Within the hollow cylinder a rod-shaped electrode made of the material to be atomized. This electrode preferably lies in the axis of the hollow cylinder and is connected, together with the hollow cylinder, to a high-frequency generator. The plasma produced by the high frequency in the hollow cylinder can be additionally condensed in an advantageous manner by a magnetic field, which permits the achievement of especially high rates of atomization. Contact coatings produced according to the invention have excellent adhesion to the support. Even in a 90 bending test, such contact coatings did not crack or flake away from the support. The microhardness values of atomized contact coatings made of high-melting, hard-to-for-m metals according to this invention are also very favorable. For example, the microhardnesses were measured on the following coatings (Vickers with 25 g. loading): Tungsten 380, molybdenum 230, ruthenium 320.

The process of the invention has also been very success ful in coating a support with a contact coating consisting of an alloy. The alloy contact coatings thus produced have the same properties as the alloy itself before it is applied, and their compositions are the same as that of the alloy before application, as determined by analysis. Even after a long period of ablation, no variation in the composition of the starting alloys was found in spite of variations in the heat of evaporation of the alloy components.

Contact coatings made of a metal carbide, boride or nitride can also be manufactured advantageously by the method of this invention. For this purpose there is added to the noble gas in the hermetically sealed vessel a known gaseous additive which reacts with the atomized metal material to form a carbide boride or nitride. The reaction product of such metal and such additive is then condensed on the support as a contact coating.

For the manufacture of large quantities of switch contact points, tongues or springs coated according to the invention it has proven to be particularly advantageous to use support materials in sheet or ribbon form, in which the portions of the surface which are not to be coated are masked olf. These support materials are then moved slowly through the stream of atomized metal particles during the coating process, for example at a short distance away from the slit of the hollow cylinder disposed in the hermetically sealed vessel. After the support materials in sheet or strip form have been coated, they are taken from the coating apparatus and the switch contacts are stamped from them. No fraying at the cut edges was observed upon stamping.

Ordinary metal support materials have proven to be serviceable bases for the coatings according to the invention, especially ferromagnetic materials such as iron-nickel alloys. German silver, brass, bronze or pure metals such as copper, silver or nickel have also proven to be adequate.

In the switch contacts manufactured according to the invention, it has proven desirable in order to achieve good results, as regards contact resistance and life expectancy to apply to the contact coating of high-melting, hard-toform metal an additional coating of a metal of the group gold, silver, platinum or palladium, or of an alloy of at least two metals of this group or of an alloy containing as principal component a metal of this group. This additional noble metal coating, whose thickness is suitably smaller than the thickness of the contact coating of highmelting, hard-to-form metal, and often amounts to only up to about of the thickness of the coating of contact material, is advantageously produced immediately after the application of the contact coating, by atomizing the noble metal or noble metal alloy, again preferably by high-frequency plasma discharge, in the same hermetically sealed vessel, in which a pressure ranging from 10- mm. Hg to 1 mm. Hg is maintained, and precipitating it onto the contact coating.

A brief description will now be given of the process according to the invention with the aid of an example of the embodiment of an apparatus for its performance which is represented diagrammatically in FIG. 1.

FIGS. 2 and 3 show vertical sections through switch contact points manufactured according to the invention.

In a hermetically sealed vessel 1 there is a hollow cylinder 2 having a slit 3. At least the inside surface of the hollow cylinder consists of the material to be atomized, although it can be made entirely of that material. The electrode 4 is disposed on the axis of the hollow cylinder. The electrode and the hollow cylinder are connected to a high-frequency generator 5. Noble gas, such as pure argon, is introduced into the vessel through the tube 7 which is equpped with a needle valve 6. By means of a vacuum pumping unit 8, a pressure ranging from 10- mm. Hg to 1 mm. Hg is maintained in the vessel 1. Above the hollow cylinder 2, at a short distance of about 10 to mm. from slit 3, there is rotatably disposed a truncatoconical body 9. On this body is wound a support 10 in strip form, which is to be coated with the contact coating according to the invention. The winding of the support 10 is so arranged in this embodiment that each succeeding turn covers a portion of the surface of the preceding turn of the support, so that only the exposed portion of the surface is coated with the contact material. Inside of the hollow cylinder 2, a high-frequency plasma discharge is produced when the high-frequency generator 5 is energized, which causes metal particles to be ablated from the hollow cylinder 2 and from the electrode 4. These metal particles pass through the slit 3 in the form of the particle stream 11 and are deposited on the exposed surface of the support band. During this coating of the support 10 according to the invention, the body 9 is slowly rotated as indicated by the arrow, so that, bit by bit, all of the exposed surface portions of the support 10 pass through the particle stream 11 and are thus coated with the contact material. When the entire support band has been coated, the body 9 is removed from the vessel 1, the support band is unwound from it, and then the switch contact points tongues or springs are stamped from the band in a normal atmosphere.

FIGS. 2 and 3 show a vertical section through switch contact points coated according to the invention. In FIG. 2, the support 10 is covered on a portion of its surface with a contact coating 12 made, for example, of highmelting, hard-to-form metal. In the switch contact point represented in FIG. 3, the contact coating 12, whose thickness is on the order of about 10 microns, for example, has deposited on its another coating of a noble metal 13. The thicknes of noble metal coating 13 amounts in this example to between about 1 micron to several microns but is less than the thickness of the contact 12.

What is claimed is:

1. A process for manufacturing a composite article having a metal support substrate and a coating on at least a portion of at least one surface of the metal support substrate of about 1 to 100 microns thick of at least one contact member selected from the group consisting of molybdenum, tungsten, rhenium, platinum, palladium, rhodium, gold, silver, ruthenium, iridium and alloys, carbides, nitrides or borides thereof, which process comprises form ing said contact member into at least the inside surface of a hollow cylinder having a longitudinal slit therein having an electrode disposed therein: positioning said metal support substrate proximate to and spaced from said slit; operatively connecting a high frequency generator to said cylinder and said electrode; providing a controllable vacuum of about 10* to 1 mm. Hg A about said substrate and said cylinder; forming a plasma in said cylinder whereby atomizing said contact member; projecting such through said slit; and depositing said atomized contact member on said metal support substrate.

2. A process as claimed in claim 1 wherein said substrate is in the form of a ribbon wrapped about a rotatable member which is rotated during said atomization and deposition.

3. A process a claimed in claim 1 including masking a portion of said metal substrate during said atomization and deposition from said contact member.

4. A process as claimed in claim 1 wherein said hollow cylinder is provided with an axial rod having on at least the surface thereof said contact metal.

5. A process as claimed in claim 1 including providing an atmosphere about said cylinder and said substrate of a gas selected from the group consisting of a noble gas, a noble gas mixed with about 20% hydrogen and a noble gas mixed with a gaseous material which reacts with said atomized contact member to form a carbide, nitride or boride.

6. A process as claimed in claim 1 wherein said contact member coating is about 5 to 30 microns thick.

7. A process as claimed in claim 1 including subjecting the composite article so produced to a second deposition of atomized metal selected from the group consisting of gold, silver, platinum, palladium or an alloy thereof to form a top coating on said contact member which is thinner than the layer of contact member.

8. A process as claimed in claim 1 wherein said metal substrate is a material selected from the group consisting of ferromagnetic materials, German silver, brass, bronze, copper, silver and nickel.

9. A process as claimed in claim 2 wherein said rotatable member is a truncated cone and wherein said wrapped ribbon partially overlaps itself as it passes about said cone.

References Cited UNITED STATES PATENTS 3,233,137 2/1'966 Anderson et al 204-192 3,250,694 5/1966 Maissel et al. 204 -192 3,458,426 7/1969 Rausch et al 204192 3,479,269 11/1969 Byrnes et al. 204192 3,528,902 9/1970 Wasa et al. 204298 JOHN H. MACK, Primary Examiner S. S. KANTER, Assistant Examiner US. Cl. X.R. 204298 

